In recent years, electronic devices have been introduced for controlling various electrical equipment in a vehicle such as an automobile. In an electric power steering apparatus as an example of electrical equipment into which an electronic device is incorporated, there is provided a motor drive unit in an enclosure accommodating an electric motor for steering an automobile and the electronic device is mounted on the motor drive unit. The electronic device is incorporated as a power module into the motor drive unit.
The power module is constituted as a so-called semiconductor module on which a power element such as a field effect transistor (FET) or an insulated gate bipolar transistor (IGBT) suitable for controlling electrical equipment driven with a relatively large current, such as an electric power steering apparatus, is mounted. Such a type of power module is also called “in-vehicle module”, because it is mounted on a vehicle.
A power element is mounted on a substrate by solder jointing when manufacturing such a semiconductor module, and a technique for electrically connecting a semiconductor chip and a lead frame using an arch-shaped metal piece is disclosed in PTL 1 and 2. In other words, the arch-shaped metal piece is bridged between an electrode pad of the semiconductor chip and an inner lead portion of the lead frame, and the metal piece and the electrode pad of the semiconductor chip, and the metal piece and the inner lead portion of the lead frame are respectively solder-jointed, so that the semiconductor chip is mounted on the lead frame.